The Heartbeat Cardiac cycle = contractions and relaxations of heart muscles in a complete heartbeat Takes ~0.8 s

4 Valves Atrioventricular (AV) valves -are tricuspid valve made of 3 flaps and bicuspid (mitral) valve made of 2 flaps - Prevents backflow into atria when ventricles contract  “lub” Semilunar valves (both pulmonary and aortic valves; half-moon shape) prevent backflow into ventricles while they relax  “dub” flaps of connective tissue prevent backflow Blood flow through valves:

Heart sound: “Lub-dub, lub-dub” Heart murmur: defective valves causing hissing sound when blood squirts backward through valves Heart sounds are caused by the closing of valves “Lub” “Dub” recoil of blood against closed AV valves recoil of blood against closed semilunar valves Lub-dub with Bill Nye:

How the heart contracts

How the heart contracts: Sinoatrial (SA) node: Pacemaker, in the wall of right atrium Sends out electrical signal causing two atria to contract simultaneously Atrioventricular (AV) node transmits signal through specialized fibres called bundle of His and Purkinje fibres Purkinje fibres initiate almost simultaneous contraction of all cells of the right and left ventricles with Bill Nye. Watch all

Electrocardiograph: records electrical impulses by a beating heart P wave = atrial contractions QRS wave = ventricular contractions T wave = ventricle recovers

“lub”“dub” The “LUB” “DUB” of Our Hearts!

LUB Omitted slide

DUB 45  the ventricles relax and the semilunar valves close to produce the second heart sound (“DUB”).  The relaxation of the ventricles is followed by the next firing of the SA node for the next heartbeat. Omitted slide

10 Heartbeat in real time MRI- imaging tool for the heart

Blood Pressure Blood pressure= force exerted on vessels’ walls as blood flows through them Pulses = evidence of artery under pressure due to heart’s contraction A digital sphymomanometer measuring blood pressure 1.Inflate the cuff to close off flow to brachial artery 2.Listening to pulse, slowly release air until pulse is heard and read the pressure – Systolic (i.e. pressure when the ventricles contract) 3.Slowly release air until no pulse is heard and then read the pressure – Diastolic (i.e. The pressure when the ventricles relax; heart is at rest) 4.Healthy = 120/80 (units = mmHg)

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Factors affecting Blood pressure Diameter of blood vessels Volume of blood Physical activity Temperature Body position Age (blood pressure usually increases with age) Stress level Diet Drinking too much alcohol Medication etc.

 Too much Na + in diet  causes H 2 O to enter blood by osmosis  increases blood volume  increases blood pressure  High blood pressure reading: above 140/90 mmHg  Stiffer arteries make heart work harder  Arteries may rupture leading to stroke, heart attack, kidney damage etc. Hypertension (high blood pressure) 14 Bypass surgery: Resource link: Diagnosis

Atherosclerosis = Hardening of the arteries Plaque (fat, cholesterol, Ca etc) built up in the artery leading to stroke, heart attack, death

Balloon angioplasty

Heart Bypass surgery